Re: How detect cycle in grammar ?

From	Borneq <a.moderacja@gmail.com>
Newsgroups	comp.compilers
Subject	Re: How detect cycle in grammar ?
Date	2011-11-24 09:24 -0800
Organization	Compilers Central
Message-ID	<11-11-050@comp.compilers> (permalink)
References	<11-11-041@comp.compilers> <11-11-045@comp.compilers>

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On 21 Lis, 19:20, Gene <gene.ress...@gmail.com> wrote:
> As I recall the algorithm starts with the lhs's of rules that expand
> entirely to terminals (including epsilon) and recursively marks
> nonterminals that have a rule where the entirely right hand side is
> either marked or terminal.  When you're done marking in this manner,
> the unmarked nonterminals are useless.  All rules involving them can
> be deleted without changing the represented language.  If the start
> symbol is unmarked, the language is empty.

I found http://programming4.us/desktop/408.aspx section "4 Reduction
of Grammar"
I interpret this: we mark nonterminal as usable if any its production
contains only terminals or marked previously nonterminals.
But what if nonterminal has one using production and one useless? For
example
A->A
A->B
B->b
How eliminate A->A ?

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How detect cycle in grammar ? Borneq <a.moderacja@gmail.com> - 2011-11-20 08:48 -0800
  Re: How detect cycle in grammar ? Hans Aberg <haberg-news@telia.com> - 2011-11-21 18:14 +0100
  Re: How detect cycle in grammar ? Gene <gene.ressler@gmail.com> - 2011-11-21 10:20 -0800
    Re: How detect cycle in grammar ? anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2011-11-22 15:20 +0000
      Re: How detect cycle in grammar ? Quinn Tyler Jackson <quinn_jackson2004@yahoo.ca> - 2011-11-25 22:28 -0800
      Re: How detect cycle in grammar ? Gene <gene.ressler@gmail.com> - 2011-11-27 10:18 -0800
    Re: How detect cycle in grammar ? Borneq <a.moderacja@gmail.com> - 2011-11-23 12:56 -0800
    Re: How detect cycle in grammar ? Borneq <a.moderacja@gmail.com> - 2011-11-24 09:24 -0800
      Re: How detect cycle in grammar ? Gene <gene.ressler@gmail.com> - 2011-11-27 10:27 -0800
        Re: How detect cycle in grammar ? anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2011-11-28 16:46 +0000
          Re: How detect cycle in grammar ? glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2011-11-29 07:31 +0000
            Re: How detect cycle in grammar ? Paul B Mann <paul@paulbmann.com> - 2011-12-01 02:46 -0800
              Re: How detect cycle in grammar ? Quinn Tyler Jackson <quinn_jackson2004@yahoo.ca> - 2011-12-02 09:20 -0800
          Re: How detect cycle in grammar ? Gene <gene.ressler@gmail.com> - 2011-12-07 06:29 -0800

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